The present invention belongs to a technical field involving an ink jet head which utilizes piezoelectric actuators to discharge ink through its nozzles, a method for fabricating the ink jet head, and an ink jet recording device.
An ink jet head which utilizes piezoelectric actuators to discharge ink is a known art, and may comprise a head main body 101 including a plurality of hollows 102 as pressure rooms each having an inlet 102a for ink supply and an outlet 102b for ink discharge as shown in FIG. 9. The hollows 102 are arranged at regular intervals in one direction (perpendicular to the paper) in the head main body 101.
The head main body 101 is composed of a pressure room component 105 forming the side walls of the hollows 102, an ink path component 106 which forms the bottom wall of the hollows 102 and is made by bonding a plurality of thin plates together, and a nozzle plate 113. The ink path component 106 includes paths 107 for ink supply and paths 108 for ink discharge, which are connected with the inlets 102a and outlets 102b, respectively. The paths 107 for ink supply are connected to an ink supply room 110 extending in the direction in which the hollows 102 are arranged, and the ink supply room 110 is connected to an ink supply hole 111, which is formed in the pressure room component 105 and ink path component 106, and is connected with an ink tank outside the drawing. The nozzle plate 113 is provided with nozzles 114 connected with the paths 108 for ink discharge.
On the top surface of the pressure room component 105 of the head main body 101, piezoelectric actuators. 121 are provided in such a manner as to block the hollows 102 of the head main body 101, thereby making up pressure rooms 103 with the hollows 102. The piezoelectric actuators 121 include piezoelectric elements 123 and top electrodes 124 provided on the surfaces of the piezoelectric elements 123 that are opposite to the pressure rooms 103 side. In addition, a bottom electrode 122 is provided on the surfaces of the piezoelectric elements 123 that are on the pressure rooms 103 side. The single bottom electrode 122 is shared by all the piezoelectric actuators 121, and also functions as a so-called diaphragm.
Applying a pulse-like voltage between the bottom electrode 122 and the top electrodes 124 causes the piezoelectric elements 123 to contract in the direction perpendicular to the direction of their thickness due to electric fields developing inside the piezoelectric elements 123. On the other hand, the bottom electrode 122 and top electrodes 124 do not contract, so that a so-called bimetal effect makes the portions of the piezoelectric actuators 121 that correspond to the pressure rooms 103 deform to bend toward the pressure rooms 3 side. This deformation generates pressure inside the pressure rooms 3, and makes the pressure discharge the ink in the pressure rooms 3 outside through the nozzles 114 via the outlets 102b and paths 108 for ink discharge.
By the way, such ink jet heads that utilize piezoelectric actuators to discharge ink through the nozzles have been variously improved in recent years to meet the stringent demands for reduction in size, driving voltage, noise, cost, improvement in ink discharge control, and the like. In order to achieve further downsizing and higher performance, it is possible to form the piezoelectric elements and electrodes into thin films, which can be micromachined easily. The easiest and most reliable method for forming these thin films is first to form the top electrodes, piezoelectric elements, and bottom electrode in this order on a substrate by spattering or deposition, then to fix the bottom electrode thus formed to the head main body, and later to eliminate the substrate by etching or another process.
However, the spattering or deposition undesirably develops foreign particles during the film formation, which cause minute defective portions in indefinite regions in the piezoelectric elements in such a manner as to be isolated by cracks from the other parts. Above all, in the case of spattering, unevenness in discharge or potential in the initial stages of the spattering can trigger to cause more such defective portions. The defective portions gradually grow as the film formation proceeds, making the cracks be extended and tapered down in the thickness direction of the piezoelectric elements. These cracks usually have approximately circular openings on both surfaces of the piezoelectric elements in their thickness direction (penetrating the piezoelectric elements in their thickness direction). Moreover, forming the bottom electrode onto the piezoelectric elements by spattering or deposition makes the bottom electrode have defective portions, which are caused by and contiguous with the defective portions in the piezoelectric elements. As a result, the bottom electrode has cracks contiguous with the cracks in the piezoelectric elements. The bottom electrode further has similar defective portions, which are caused in regions not contiguous with the defective portions of the piezoelectric elements. When the bottom electrode is made from chrome preferably used for its excellent ink discharge performance and other characteristics in order to function the electrode as a diaphragm, defective portions occur much more easily. Although the occurrence of these defective portions can be restricted to some extent, it is difficult to eliminate them completely.
The presence of the defective portions (cracks) in the piezoelectric elements decreases their mechanical strength, and increases the intensity of the electric fields in the cracks, thereby promoting leaks. The presence of cracks in the bottom electrode decreases its mechanical strength, and makes it impossible to uniformly apply a voltage on the entire piezoelectric elements. Moreover, if the ink in the pressure rooms happens to be in contact with the piezoelectric elements via the cracks in the bottom electrode, the piezoelectric elements may be melted or damaged in other ways, depending on the material of the ink. If cracks are formed contiguously across the piezoelectric elements and bottom electrode, intrusion by ink having less electric insulation than the piezoelectric elements may cause a short between the bottom and top electrodes, so as to produce a dielectric breakdown.
The present invention has been contrived in view of these aspects, and its object is that when an ink jet head is downsized by forming the piezoelectric elements and electrodes of the piezoelectric actuators into thin films, the piezoelectric actuators are prevented from malfunctioning due to the cracks developing in the piezoelectric elements or electrodes during the film formation, so as to increase their durability.
In order to achieve the above-mentioned object, according to the present invention, the piezoelectric actuators, which include piezoelectric elements, first electrodes provided on the surfaces of the piezoelectric elements that are opposite to the pressure rooms side, and a second electrode provided on the other surfaces of the piezoelectric elements that are on the pressure rooms side, further comprise either a crack covering member or an ink contact prevention member either on the surface of the second electrode that is on the pressure rooms side or on the surfaces of the piezoelectric elements that are on the second electrode side. The crack covering member is made from an electric insulating material, which is used to fill a crack, whereas the ink contact prevention member prevents the ink in the pressure rooms from being in contact with the piezoelectric elements via the crack in the second electrode.
To be more specific, the first invention relates to an ink jet head comprising: a head main body including a hollow as a pressure room having an inlet for ink supply and an outlet for ink discharge, and a nozzle leading to the outlet; and a piezoelectric actuator which is arranged to block said hollow and make up the pressure room together with said hollow and which includes a piezoelectric element, a first electrode arranged on a surface of the piezoelectric element that is opposite to the pressure room side, and a second electrode arranged on other surface of the piezoelectric element that is on the pressure room side, said piezoelectric actuator making the pressure room deform to decrease its capacity by applying a voltage onto the piezoelectric element via the first electrode and second electrode, thereby discharging ink contained inside the pressure room through the outlet, wherein a crack covering member made from an electric insulating material is arranged on a surface of the piezoelectric element of said piezoelectric actuator that is on the second electrode side in such a manner as to fill said electric insulating material into a crack which is open on the surface of the piezoelectric element that is on the second electrode side.
In the above structure, filling the electric insulating material into the crack in the piezoelectric element not only maintains the mechanical strength of the piezoelectric element but also prevents leaks in the crack. As a result, even if forming the piezoelectric element and other components by spattering or deposition causes a crack in the piezoelectric element, the crack does not cause the piezoelectric actuator to malfunction, so that excellent ink discharge performance can be maintained for a long period of time.
According to the second invention, in the ink jet head of the first invention, said crack covering member is formed as a layer on the surface of the piezoelectric element that is on the second electrode side.
This structure makes it possible, when there are a plurality of cracks, to fill the electric insulting material into all cracks at once while forming the layer on the surface of the piezoelectric element that is on the second electrode side, making it unnecessary to provide every one of the cracks with the crack covering member. Furthermore, even if the ink in the pressure room intrudes into the crack in the second electrode, the piezoelectric element is blocked against the ink by the layer. -In addition, since the ink never intrudes into the crack in the piezoelectric element, there is no occurrence of a short between the first and second electrodes even if the ink has lower electric insulation than the piezoelectric element. Although the crack covering member in the form of a layer may lower the electric field generated on the piezoelectric element, a predetermined electric field can be generated by making the layer thin enough.
The third invention relates to an ink jet head comprising: a head main body including a hollow as a pressure room having an inlet for ink supply and an outlet for ink discharge, and a nozzle leading to the outlet; and a piezoelectric actuator which is arranged to block said hollow and make up the pressure room together with said hollow and which includes a piezoelectric element, a first electrode arranged on a surface of the piezoelectric element that is opposite to the pressure room side, and a second electrode arranged on other surface of the piezoelectric element that is on the pressure room side, said piezoelectric actuator making the pressure room deform to decrease its capacity by applying a voltage onto the piezoelectric element via the first electrode and second electrode, thereby discharging ink contained inside the pressure room through the outlet, wherein a crack covering member made from an electric insulating material is provided on a surface of the second electrode of said piezoelectric actuator that is on the pressure room side in such a manner as to fill said electric insulating material into a crack which is open on the surface of the second electrode that is on the pressure room side and which is contiguous across the second electrode and piezoelectric element.
In this structure, filling the electric insulating material into a crack, which is contiguous across the second electrode and piezoelectric element, not only maintains the mechanical strength of the second electrode and piezoelectric element but also prevents leaks in the crack in the piezoelectric element. In addition, there is no intrusion by ink into the crack contiguous across the second electrode and piezoelectric element, thereby protecting the piezoelectric element against intrusion by the ink. As a result, similar to the first invention, the durability of the piezoelectric actuators can be increased.
According to the fourth invention, in the ink jet head of the third invention, said crack covering member is formed as a layer on the surface of the second electrode that is on the pressure room side.
This structure facilitates the filling of the electric insulating material into every crack. Furthermore, even if the second electrode has an additional crack in a region not contiguous with the crack in the piezoelectric element, the ink is prevented from intruding into the additional crack, thereby securing the protection of the piezoelectric element against intrusion of the ink.
The fifth invention relates to an ink jet head comprising: a head main body including a hollow as a pressure room having an inlet for ink supply and an outlet for ink discharge, and a nozzle leading to the outlet; and a piezoelectric actuator which is arranged to block said hollow and make up the pressure room together with said hollow and which includes a piezoelectric element, a first electrode arranged on a surface of the piezoelectric element that is opposite to the pressure room side, and a second electrode arranged on other surface of the piezoelectric element that is on the pressure room side, said piezoelectric actuator making the pressure room deform to decrease its capacity by applying a voltage onto the piezoelectric element via the first electrode and second electrode, thereby discharging ink contained inside the pressure room through the outlet, wherein an ink contact prevention member is formed as a layer on the surface of the piezoelectric element of said piezoelectric actuator that is on the second electrode side so as to prevent the piezoelectric element from being in contact with the ink inside the pressure room via a crack penetrating the second electrode in a thickness direction thereof.
This structure can protect the piezoelectric element against intrusion by the ink, thereby increasing the durability of the piezoelectric actuator. If there is no occurrence of a crack in the portion of the piezoelectric element that is between the first and second electrodes, an approximately uniform electric field can be generated on the entire piezoelectric element by making the ink contact prevention layer from a conductive material.
The sixth invention relates to an ink jet head comprising: a head main body including a hollow as a pressure room having an inlet for ink supply and an outlet for ink discharge, and a nozzle leading to the outlet; and a piezoelectric actuator which is arranged to block said hollow and make up the pressure room together with said hollow and which includes a piezoelectric element, a first electrode arranged on a surface of the piezoelectric element that is opposite to the pressure room side, and a second electrode arranged on other surface of the piezoelectric element that is on the pressure room side, said piezoelectric actuator making the pressure room deform to decrease its capacity by applying a voltage onto the piezoelectric element via the first electrode and second electrode, thereby discharging ink contained inside the pressure room through the outlet, wherein an ink contact prevention member is formed on the surface of the second electrode of said piezoelectric actuator that is on the pressure room side so as to prevent the piezoelectric element from being in contact with the ink inside the pressure room via a crack penetrating the second electrode in a thickness direction thereof.
This structure can protect the piezoelectric element against intrusion of the ink, thereby increasing the durability of the piezoelectric actuator.
According to the seventh invention, in the ink jet head of the sixth invention, said ink contact prevention member is formed as a layer on the surface of the second electrode that is on the pressure room side.
This structure eliminates the necessity of providing the ink contact prevention member to each of the plural cracks, which facilitates the protection of the piezoelectric element against intrusion of the ink. If there is no occurrence of a crack in the portion of the piezoelectric element that is between the first and second electrodes, an approximately uniform electric field can be generated on the entire piezoelectric element by making the ink contact prevention member formed as a layer from a conductive material and filling the conductive material into the crack in the second electrode.
The eighth invention relates to a method for fabricating an ink jet head comprising a pressure room which contains ink, a nozzle leading to the pressure room, a first electrode arranged on one side and a second electrode arranged on other side of a piezoelectric element in a thickness direction thereof, and a piezoelectric actuator which discharges the ink contained in the pressure room through the nozzle by applying a voltage onto the piezoelectric element via the first electrode and second electrode, said method comprising the steps of: forming the first electrode on a substrate; forming the piezoelectric element on the first electrode; forming a crack covering layer made from an electric insulating material on the piezoelectric element while filling said electric insulating material into a crack which is open on a top surface of the piezoelectric element; forming the second electrode on said crack covering layer; fixing the second electrode to a pressure room forming member having a space for the pressure room; and removing the substrate after said fixing step.
This structure easily realizes the ink jet head of the second invention.
The ninth invention relates to a method for fabricating an ink jet head comprising a pressure room which contains ink, a nozzle leading to the pressure room, a first electrode arranged on one side and a second electrode arranged on other side of a piezoelectric element in a thickness direction thereof, and a piezoelectric actuator which discharges the ink contained in the pressure room through the nozzle by applying a voltage onto the piezoelectric element via the first electrode and second electrode, said method comprising the steps of: forming the first electrode on a substrate; forming the piezoelectric element on the first electrode; forming the second electrode on the piezoelectric element; forming a crack covering layer made from an electric insulating material on the second electrode, while filling said electric insulating material into a crack which is open on a top surface of the second electrode and which is contiguous across the second electrode and piezoelectric element; fixing said crack covering layer to a pressure room forming member having a space for the pressure room; and removing the substrate after said fixing step.
This structure easily realizes the ink jet head of the fourth invention.
The tenth invention relates to a method for fabricating an ink jet head comprising a pressure room which contains ink, a nozzle leading to the pressure room, a first electrode arranged on one side and a second electrode arranged on other side of a piezoelectric element in a thickness direction thereof, and a piezoelectric actuator which discharges the ink contained in the pressure room through the nozzle by applying a voltage onto the piezoelectric element via the first electrode and second electrode, said method comprising the steps of: forming the first electrode on a substrate; forming the piezoelectric element on the first electrode; forming an ink contact prevention layer on the piezoelectric element; forming the second electrode on. said ink contact prevention layer; fixing the second electrode to a pressure room forming member having a space for the pressure room; and removing the substrate after said fixing step, wherein said ink contact prevention layer prevents the ink contained in the pressure room from being in contact with the piezoelectric element via a crack penetrating the second electrode in a thickness direction thereof.
This structure easily realizes the ink jet head of the fifth invention.
The eleventh invention relates to a method for fabricating an ink jet head comprising a pressure room which contains ink, a nozzle leading to the pressure room, a first electrode arranged on one side and a second electrode arranged on other side of a piezoelectric element in a thickness direction thereof, and a piezoelectric actuator which discharges the ink contained in the pressure room through the nozzle by applying a voltage onto the piezoelectric element via the first electrode and second electrode, said method comprising the steps of: forming the first electrode on a substrate; forming the piezoelectric element on the first electrode; forming the second electrode on the piezoelectric element; forming an ink contact prevention layer on the second electrode; fixing said ink contact prevention layer to a pressure room forming member having a space for the pressure room; and removing the substrate after said fixing step, wherein said ink contact prevention layer prevents the ink contained in the pressure room from being in contact with the piezoelectric element via a crack penetrating the second electrode in a thickness direction thereof.
This structure easily realizes the ink jet head of the seventh invention.
The twelfth invention relates to a method for fabricating an ink jet head comprising a pressure room which contains ink, a nozzle leading to the pressure room, a first electrode arranged on one side and a second electrode arranged on other side of a piezoelectric element in a thickness direction thereof, and a piezoelectric actuator which discharges the ink contained in the pressure room through the nozzle by applying a voltage onto the piezoelectric element via the first electrode and second electrode, said method comprising the steps of: forming the first electrode on a substrate; forming the piezoelectric element on the first electrode; forming a crack covering layer made from an electric insulating material on the piezoelectric element, while filling said electric insulating material into a crack occurring in the piezoelectric element in such a manner as to be open on a top surface of the piezoelectric element; forming the second electrode on the piezoelectric element; forming an ink contact prevention layer on the second electrode; fixing said ink contact prevention layer to a pressure room forming member having a space for the pressure room; and removing the substrate after said fixing step, wherein said ink contact prevention layer prevents the ink contained in the pressure room from being in contact with the piezoelectric element via a crack penetrating the second electrode in a thickness direction thereof.
This structure provides the crack covering layer on the surface of the piezoelectric element that is on the second electrode side, and the ink contact prevention layer on the surface of the second electrode that is on the pressure room side. As a result, even if cracks occur in both the piezoelectric element and second electrode, it is secured to prevent the cracks from causing the piezoelectric actuator to malfunction, thereby increasing its durability.
The thirteenth invention relates to an ink jet recording device comprising: an ink jet head composed of a head main body including a hollow as a pressure room having an inlet for ink supply and an outlet for ink discharge, and a nozzle leading to the outlet, and a piezoelectric actuator which is arranged to block said hollow and make up the pressure room together with said hollow and which includes a piezoelectric element, a first electrode arranged on a surface of the piezoelectric element that is opposite to the pressure room side, and a second electrode arranged on other surface of the piezoelectric element that is on the pressure room side, said piezoelectric actuator making the pressure room deform to decrease its capacity by applying a voltage onto the piezoelectric element via the first electrode and second electrode, thereby discharging ink contained inside the pressure room through the outlet; and relative transfer means for transferring said ink jet head and a recording medium relatively, wherein recording is performed by directing jets of ink at the recording medium through the nozzle of the head main body of said ink jet head, while said ink jet head is being transferred relatively to the recording medium by said relative transfer means.
Said ink jet recording device further comprises a crack covering member made from an electric insulating material and arranged on a surface of the piezoelectric element of said piezoelectric actuator of said ink jet head that is on the second electrode side in such a manner as to fill said electric insulating material into a crack which is open on the surface of the piezoelectric element that is on the second electrode side.
This invention offers the same effects as the first invention.
The fourteenth invention relates to an ink jet recording device comprising: an ink jet head composed of a head main body including a hollow as a pressure room having an inlet for ink supply and an outlet for ink discharge, and a nozzle leading to the outlet, and a piezoelectric actuator which is arranged to block said hollow and make up the pressure room together with said hollow and which includes a piezoelectric element, a first electrode arranged on a surface of the piezoelectric element that is opposite to the pressure room side, and a second electrode arranged on other surface of the piezoelectric element that is on the pressure room side, said piezoelectric actuator making the pressure room deform to decrease its capacity by applying a voltage onto the piezoelectric element via the first electrode and second electrode, thereby discharging ink contained inside the pressure room through the outlet; and relative transfer means for transferring said ink jet head and a recording medium relatively, wherein recording is performed by directing jets of ink at the recording medium through the nozzle of the head main body of said ink jet head, while said ink jet head is being transferred relatively to the recording medium by said relative transfer means.
Said ink jet recording device further comprises a crack covering member made from an electric insulating material and arranged on a surface of the second electrode of said piezoelectric actuator of said ink jet head that is on the pressure room side in such a manner as to fill said electric insulating material into a crack which is open on the surface of the second electrode that is on the pressure room side and which is contiguous across the second electrode and piezoelectric element.
This invention offers the same effects as the third invention.
The fifteenth invention relates to an ink jet recording device comprising: an ink jet head composed of a head main body including a hollow as a pressure room having an inlet for ink supply and an outlet for ink discharge, and a nozzle leading to the outlet, and a piezoelectric actuator which is arranged to block said hollow and make up the pressure room together with said hollow and which includes a piezoelectric element, a first electrode arranged on a surface of the piezoelectric element that is opposite to the pressure room side, and a second electrode arranged on other surface of the piezoelectric element that is on the pressure room side, said piezoelectric actuator making the pressure room deform to decrease its capacity by applying a voltage onto the piezoelectric element via the first electrode and second electrode, thereby discharging ink contained inside the pressure room through the outlet; and relative transfer means for transferring said ink jet head and a recording medium relatively, wherein recording is performed by directing jets of ink at the recording medium through the nozzle of the head main body of said ink jet head, while said ink jet head is being transferred relatively to the recording medium by said relative transfer means.
Said ink jet recording device further comprises a crack covering member made from an electric insulating material and arranged as a layer on a surface of the piezoelectric element of said piezoelectric actuator of said ink jet head that is on the second electrode side so as to prevent the ink contained in the pressure room from being in contact with the piezoelectric element, via a crack penetrating the second electrode in a thickness direction thereof.
This structure offers the same effects as the fifth invention.
The sixteenth invention relates to an ink jet recording device comprising: an ink jet head composed of a head main body including a hollow as a pressure room having an inlet for ink supply and an outlet for ink discharge, and a nozzle leading to the outlet, and a piezoelectric actuator which is arranged to block said hollow and make up the pressure room together with said hollow and which includes a piezoelectric element, a first electrode arranged on a surface of the piezoelectric element that is opposite to the pressure room side, and a second electrode arranged on other surface of the piezoelectric element that is on the pressure room side, said piezoelectric actuator making the pressure room deform to decrease its capacity by applying a voltage onto the piezoelectric element via the first electrode and second electrode, thereby discharging ink contained inside the pressure room through the outlet; and relative transfer means for transferring said ink jet head and a recording medium relatively, wherein recording is performed by directing jets of ink at the recording medium through the nozzle of the head main body of said ink jet head, while said ink jet head is being transferred relatively to the recording medium by said relative transfer means.
Said ink jet recording device further comprises an ink contact prevention member arranged on a surface of the second electrode of said piezoelectric actuator of said ink jet head that is on the pressure room side so as to prevent the ink contained in the pressure room from being in contact with the piezoelectric element via a crack penetrating the second electrode in a thickness direction thereof.
This structure offers the same effects as the sixth invention.